1. Technical Field
The invention relates to a polarizer for exciting the parabolic reflector of a directional antenna which includes a profile section which is formed as a waveguide and adapted to simultaneously transmit two linearly polarized orthogonal electromagnetic waves. Two rectangular waveguides separately guide the two electromagnetic waves and are connected to the profile section. The end face of one of the rectangular waveguides is connected to the side wall of the profile section in the radial direction, whereas the other rectangular waveguide is connected to an end face of the profile section. Both rectangular waveguides are electromagnetically connected to the profile section via openings, with a short circuit element disposed in the profile section between the openings.
2. Description of the Prior Art
Directional antennae are used for wireless transmission of electromagnetic waves from one location to another location and employed with, for example, microwave radio links, satellite communication and radio position fixing. Their efficiency has to be as high as possible. Directional antennae are equipped with primary radiators and must strongly attenuate the side lobes in the interfering directions and provide good matching and high gain. The primary radiators are typically equipped with a feed horn and located in the focal point of parabolic antenna. However, the antenna can also be a so-called backfire antenna equipped with a subreflector. Some conventional antennae can also handle two electromagnetic waves which are separated from each other. Such antennae employ a polarizer which is connected to two feed lines which separately carry the two waves.
A polarizer of this type, which is simultaneously the primary radiator, is known from U.S. Pat. No. 3,864,688. The two feed lines therein are formed as rectangular waveguides and are connected coplanarly to the tubular polarizer. This configuration allows the two feed lines to be arranged sequentially in the same plane. This type of arrangement, however, has the disadvantage that the polarizer, which is to separate the two waves, requires complex and precise machining because one wave must be rotated by 90.degree. without being reflected and interfering with the other wave. To accomplish this, the conventional polarizer has pins or a twisted sheet metal strip which are located between the two feed locations of the two waveguides pins and which are offset in both the axial and the circumferential direction.
In the polarizer described in DE 32 41 890 C2, and corresponding U.S. Pat. No. 4,584,588, which is also used as a primary radiator, the two waves are separated with a simpler device. Here, one of the flat sides of the second rectangular waveguide is connected to the end face of the polarizer. The end face is closed off by the second rectangular waveguide. Consequently, the two rectangular waveguides are connected to the polarizer so that polarization direction of one waveguide is offset by 90.degree. with respect to the other waveguide. The two waves are thus fed orthogonal to each other and are therefore completely decoupled. No additional components are required. Adjustable tuning or trimming elements 9, 10 are employed to couple the waves in and out while minimizing reflections.